The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation and techniques for preparing an intervertebral disc space for insertion of a spinal implant between adjacent vertebra.
Various surgical methods have been devised for the implantation of fusion devices into the disc space. These methods include anterior, lateral, postero-lateral and posterior approaches to the subject disc space. Many traditional surgical procedures for correction of disc space pathologies can cause significant trauma to the intervening tissues. These open procedures often require a long incision, extensive muscle stripping, prolonged retraction of tissues, denervation and devascularization of tissue. Most of these surgeries require room time of several hours and several weeks of post-operative recovery time due to the use of general anesthesia and the destruction of tissue during the surgical procedure. In some cases, these invasive procedures lead to permanent scarring and pain that can be more severe than the pain leading to the surgical intervention. Instruments that can be used in open procedures that minimize disruption to tissue and nerves surrounding the disc space, yet provide safe and effective disc space preparation during the open procedure would thus be desirable.
Minimally invasive surgical techniques are particularly desirable for spinal and neurosurgical applications because of the need for access to locations deep within the body and the danger of damage to vital intervening tissues. The development of percutaneous spinal procedures has yielded a major improvement in reducing recovery time and post-operative pain because they require minimal, if any, muscle dissection and they can be performed under local anesthesia. One drawback associated with minimally invasive procedures is the relatively small amount of working space available to the surgeon adjacent the cannula or sleeve providing access to the surgical site.
What is therefore needed is instruments and techniques that provide for safe and effective disc space preparation and implant insertion while minimizing trauma to tissue surrounding the surgical site. While the more recent techniques and instrumentation represent an advance over earlier surgical procedures for the preparation of the disc space for insertion of spinal implants, the need for improvement still remains. The present invention is directed to these needs, among others, and provides convenient methods and instruments for use in preparing a disc space for placement of an implant therein.
One aspect of the present invention is to provide a shim with a thin blade to provide and maintain bi-lateral distraction of a disc space during disc space preparation. The shim comprises a blade and a shaft having a first end connected to the blade and an opposite second end.
Another aspect of the present invention provides a shim that maintains disc space distraction during subsequent spinal procedures for insertion of a spinal implant. The shim includes a blade and a shaft having a first end connected with the blade. The blade has a length extending between a leading end and a trailing end, a height extending between a top and bottom surface, and a width between a first side and a second side of the blade. In one embodiment, the blade has a height to thickness ratio that is greater than 3. In another embodiment, the leading end of the blade is rounded. In yet another embodiment, the trailing end of the blade has a pair of shoulders at the connection with the shaft. In still a further embodiment, the shaft is bendable and has a second end that is configured for connection to an arm engaged to a surgical table. In yet another embodiment, the shim is used in an endoscopically assisted approach and the shaft has a sufficient length to extend through a cannula.
Still a further aspect to the present invention is to provide a spinal disc space shim assembly. The shim assembly includes a shim and a driver for driving the shim into the distracted disc space. The shim includes a blade and a shaft having a first end connected to the blade. A shoulder is formed at the connection between the blade and the shaft. The driver includes a channel at its distal end slidably disposed about the shaft of the shim. The channel has a driving end that impacts the shoulder as the driver is manipulated to impact the shim and drive the blade to a desired depth in the disc space.
In another aspect of the present invention, a method for maintaining disc space distraction during disc space preparation via posterior access to the spine is provided. The method comprising exposing a portion of the dura and retracting the dura and tissue to expose underlying spinal elements. A disc space distractor is inserted on the side of the disc space to distract the disc space to the desire height. A shim having a blade connected to a shaft is inserted on the side of the disc space distractor opposite the nerve root retractor. The blade is sized to maintain the distraction height of the disc space. The disc space distractor is then removed and procedures for preparing the disc space for implant insertion are completed between the nerve root retractor and the disc distractor. In another embodiment, the shim is also inserted on the side of the retractor holding the dura to maintain parallel disc space distraction.
According to another aspect of the invention a method for maintaining disc space distraction is provided. The method includes exposing a portion of the spine at the disc space and bi-laterally distracting the disc space to a desired height with a pair of bi-lateral disc distractors. A first shim is selected that includes a shaft connected to a blades the blade having a height between a top surface and a bottom surface that corresponds to the distracted disc space height and a thickness between a first side surface and a second side surface. The first shim is inserted into the disc space with one of the side surfaces positioned along one of the pair of bi-lateral disc distractors. The first disc distractor is then removed from the disc space. A second shim is selected that includes a shaft connected with a blade. The blade has a height between a top surface and a bottom surface that corresponds to the distracted disc space height and a thickness between a first side surface and a second side surface. The second shim is inserted into the disc space with one side surface along the other of the pair of bi-lateral disc distractors. The second disc distractor is removed from the disc space and subsequent procedures performed in the distracted disc space between the first and second shims.
The present invention also contemplates a method of preparing a disc space and inserting an implant. The method utilizes one or more of the instruments described above to prepare the disc space for receiving an implant.